Kotlin sortBy sortedBysortedWithsortWith区别

Posted 2022-11-11 aikongmeng

源码

import kotlin.test.*

fun main(args: Array<String>) 

val list = mutableListOf("aaa", "cc", "bbbb")
val sorted = list.sortedBy  it.length 

println(list) // [aaa, cc, bbbb]
println(sorted) // [cc, aaa, bbbb]
list.sortBy it.length
println(list)//[cc, aaa, bbbb]

sortBy Sorts elements in the list 就地排序

/**
 * Sorts elements in the list in-place according to natural sort order of the value returned by specified [selector] function.
 * 
 * The sort is _stable_. It means that equal elements preserve their order relative to each other after sorting.
 */
public inline fun <T, R : Comparable<R>> MutableList<T>.sortBy(crossinline selector: (T) -> R?): Unit 
    if (size > 1) sortWith(compareBy(selector))

sortedBy Returns a list of all elements sorted 返回新的list

/**
 * Returns a list of all elements sorted according to natural sort order of the value returned by specified [selector] function.
 * 
 * The sort is _stable_. It means that equal elements preserve their order relative to each other after sorting.
 * 
 * @sample samples.collections.Collections.Sorting.sortedBy
 */
public inline fun <T, R : Comparable<R>> Iterable<T>.sortedBy(crossinline selector: (T) -> R?): List<T> 
    return sortedWith(compareBy(selector))

expect fun <T> MutableList<T>.sortWith(comparator: Comparator<in T>): Unit

/**
 * Returns a list of all elements sorted according to the specified [comparator].
 * 
 * The sort is _stable_. It means that equal elements preserve their order relative to each other after sorting.
 */
public fun <T> Iterable<T>.sortedWith(comparator: Comparator<in T>): List<T> 
    if (this is Collection) 
       if (size <= 1) return this.toList()
       @Suppress("UNCHECKED_CAST")
       return (toTypedArray<Any?>() as Array<T>).apply  sortWith(comparator) .asList()
    
    return toMutableList().apply  sortWith(comparator)